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Raise exception in read_csv when prefix is set, but not used because a header exists #27998

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Raise exception in read_csv when prefix is set, but not used because a header exists #27998

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PraneethKhanna
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@PraneethKhanna PraneethKhanna commented Aug 18, 2019 •
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Raised an error if argument prefix is set when there are headers present during pandas read_csv.

@PraneethKhanna
GH27394
ae942f3 
Raised an error if argument prefix is set when there are headers present during pandas read_csv.
mroeschke
mroeschke requested changes Aug 18, 2019
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Needs test and whatsnew entry in 1.0.0

@datapythonista datapythonista changed the title GH27394 Raise exception in read_csv when prefix is set, but not used because a header exists Aug 19, 2019
@datapythonista datapythonista added Error Reporting Incorrect or improved errors from pandas IO CSV read_csv, to_csv labels Aug 19, 2019
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datapythonista reviewed Aug 19, 2019
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This change can break code, not sure if we should start by a warning and break later.

pandas/io/parsers.py Outdated
@@ -1930,6 +1930,9 @@ def __init__(self, src, **kwds):
]
else:
self.names = list(range(self._reader.table_width))
else:
if self.prefix:
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probably worth using elif

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yes, will change that

pandas/io/parsers.py Outdated
@@ -1930,6 +1930,9 @@ def __init__(self, src, **kwds):
]
else:
self.names = list(range(self._reader.table_width))
else:
if self.prefix:
raise ValueError("argument prefix must be None if header not None")
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The error message is not 100% correct, since the header can be provided with names.

@PraneethKhanna
GH27998
2a1173c 
Raised the appropriate error message
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@PraneethKhanna do you have time to add the requested test and the note in the release notes (aka whatsnew)?

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WillAyd commented Sep 17, 2019

Looks like this is stale but @PraneethKhanna if you'd like to pick back up please ping!

@WillAyd WillAyd closed this Sep 17, 2019
@TomAugspurger TomAugspurger mentioned this pull request Oct 19, 2019
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pd.read_csv prefix parameter seems do not works
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@PraneethKhanna @datapythonista @WillAyd @mroeschke